The present invention relates to methods of machining aluminum. It especially relates to methods of machining internal and external grooves and threads in aluminum.
While a variety of tool materials, such as physical vapor deposition TiN coated cemented carbides (e.g., KC730) and diamond tipped tools (e.g., KD100), have been used in the past to machine certain aluminum based alloys, diamond tipped tools are regarded as being the best in terms of tool lifetime and parts machined per cutting edge. In particular, for machining high silicon aluminum alloys, such as the 3xx.x and 4xx.x series of cast aluminum alloys, and the 4xxx wrought aluminum alloys (see "Metals Handbook," Volume 2, 10th Edition, ASM International (1990), Pages 15-28), only diamond tipped tools, such as KD100, are recommended for machining grooves or threads in these materials (see "Kennametal, Tools, Tooling Systems, Services for the Global Metalworking Industry," Kennametal Inc. (1991), Pages 275, 276, 372 and 392-396). KC730 and KD100 are trademarks of Kennametal Inc. and are used as such herein. An example of cast high silicon aluminum alloys are the 380 type alloys which typically have about 7.5 to 9.5 weight percent silicon in addition to other alloying elements.
A polycrystalline diamond tipped tool was used to machine an inside diameter oil seal groove (having a width of 2.73 mm) in an automobile transmission component, a piston made of cast 380 aluminum alloy. The polycrystalline diamond grooving tool made the approximately 3 to 5 mm deep plunge cut for the groove at a feed rate of 0.076 mm/revolution and a speed of 1628 revolutions per minute (i.e., at about 950 to 1110 surface feet per minute), using flood coolant. The inside diameter at the location of the groove went from an original diameter of about 56.6 to 59.9 mm to about 66.1 mm after the groove was machined. During the cut, however, an extremely thin, practically invisible chip, almost like cellophane, would weld itself to 20 to 90 degrees of the bottom circumference of the groove, which was unacceptable.